Vector biologists are rapidly recognizing that individual mosquitoes within a natural population show a great amount of variation. Some of the variable factors are determinants of vector potential, and are correlated with adult mosquito body size. The purpose of this proposed research is to study field populations of Aedes aegypti and Culex quinquefasciatus to establish a quantitative relationship among adult mosquito size and certain behavioral and ecological parameters related to vector potential. The specific goals of this proposal are to: 1. Quantify naturally occurring patterns in adult mosquito body size and identify environmental qualities related to changes in the body size distribution of a mosquito population. 2. Examine the relationships among adult body size and factors influencing the vector potential of a mosquito population such as longevity, blood-feeding success, nectar feeding, persistence in blood feeding, and caloric reserves. 3. Produce a laboratory reared population of mosquitoes with the same body size distribution and with biological qualities (survival, blood-feeding persistence, caloric reserves, etc.) similar to those found in field populations. The results of this work will identify qualities determining vector potential that can be monitored by observing the body size distribution in field populations of mosquitoes. Also, the establishment of laboratory - rearing procedures to produce mosquitoes with qualities similar to those of field populations will insure that future work with laboratory stocks will be biologically relevant.